1. Field of the Invention
The invention relates to a recording information reproducing apparatus for reproducing recording information from a recording medium.
2. Description of Background Information
An example of the construction of a CD (compact disk) player, as a recording information reproducing apparatus, is schematically illustrated in FIG. 1.
As shown in FIG. 1, a pickup 1 irradiates a light beam to a compact disk 3 as a recording medium which is rotated by a spindle motor 2. In this instance, the pickup 1 receives the reflected light from the compact disk 3 and generates a read signal having a signal level according to the amount of light reception. A head amplifier 4 amplifies the read signal to a desired level and supplies a resultant amplification read signal to a waveform equalizing circuit 5.
The waveform equalizing circuit 5 executes waveform compensation an the amplification read signal by frequency characteristics for emphasizing a predetermined high frequency band of the amplification read signal and supplies the resultant signal to a comparator 6. Namely, the waveform equalizing circuit 5 increases an amplitude of the high frequency component in order to compensate a reduction of the amplitude in the high frequency component of the read signal which occurs in an optical reproducing system of the CD player. In the reproduction of the optical disk, although an amplitude reduction amount generally enlarges as a recording density of the optical disk rises, it is sufficient to use a fixed gain characteristic of a high frequency band in the waveform equalizing circuit 5 because the data is recorded at an almost constant recording density on the compact disk 3.
The comparator 6 compares the signal level of the read signal which has been waveform compensated by the waveform equalizing circuit 5 with a predetermined reference voltage and generates a binary signal according to the comparison result. A clock generating circuit 7 generates a clock signal whose phase is synchronized with a signal edge of the binary signal and supplies it to a sampling circuit 8. The sampling circuit 8 samples the binary signal at a timing according to the clock signal and sequentially generates the sampled values as reproduced digital signals.
In the CD player mentioned above, by using the waveform equalizing circuit 5, the high frequency characteristics of the read signal are compensated for thereby improving information reading precision.
In recent years, a DVD (Digital Video Disk) in which not only a digital audio signal but also a digital video signal are recorded onto a recording disk of a compact size at a high density has been proposed.
In an SD system (Super Density disk system) as one system of such a DVD, the use of a plurality of kinds of recording disks having different recording densities has been proposed. As a recording information reproducing apparatus corresponding to the SD system, it is desired that the reproducing operation can be performed for any one of a plurality of kinds of recording disks having different recording densities.
As mentioned above, however, since an amplitude reduction amount of the high frequency band in the read signal differs in accordance with the recording density of the recording disk as a target for reproduction, even if the waveform equalizing circuit 5 as shown in FIG. 1 is applied to the recording information reproducing apparatus corresponding to the SD system, a proper waveform compensation corresponding to all kinds is not performed, so that there arises a problem that the digital signal cannot be reproduced at high accuracy.